Magnetic material filled printed circuit boards and printed circuit board stators

ABSTRACT

A dielectric substrate may support conductive traces that form windings for a least one pole of a planar armature of an axial flux machine. At least a portion of the dielectric substrate, which is adapted to be positioned within an annular active area of the axial flux machine, may include a soft magnetic material. Such a planar armature may be produced, for example, by forming the conductive traces on the dielectric substrate, and filling interstitial gaps between the conductive traces with at least one epoxy material in which the soft magnetic material is embedded.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 119(e) of U.S.Provisional Application No. 63/227,644, entitled MAGNETIC MATERIALFILLED PRINTED CIRCUIT BOARDS AND PRINTED CIRCUIT BOARD STATORS, filedJul. 30, 2021, the entire content of which is incorporated herein byreference.

BACKGROUND

Permanent magnet axial flux motors and generators described by severalpatents, such as U.S. Pat. No. 7,109,625 (“the '625 patent”) and U.S.Pat. No. 10,170,953 (“the '953 patent”), the entire contents of whichare incorporated herein by reference, feature a planar printed circuitboard stator assembly between rotors.

SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features, nor is it intended to limit the scope of the claimsincluded herewith.

In accordance with one example embodiment, a planar armature for anaxial flux machine comprises a dielectric substrate including at least afirst portion that is adapted to be positioned within an annular activearea of the axial flux machine, wherein at least the first portioncomprises a soft magnetic material, and further comprises conductivetraces supported by the dielectric substrate, the conductive tracesforming windings for a least one pole of the planar armature.

In accordance with another example embodiment, a printed circuit boardcomprises a dielectric substrate, and conductive traces supported by thedielectric substrate, wherein at least a first portion of the dielectricsubstrate comprises a soft magnetic material.

In accordance with still another example embodiments, a method forforming a planar armature for an axial flux machine comprises formingconductive traces on a dielectric substrate, the conductive tracesforming windings for a least one pole of the planar armature, andfilling interstitial gaps between the conductive traces with at leastone epoxy material in which soft magnetic material is embedded.

BRIEF DESCRIPTION OF THE DRAWINGS

Objects, aspects, features, and advantages of embodiments disclosedherein will become more fully apparent from the following detaileddescription, the appended claims, and the accompanying figures in whichlike reference numerals identify similar or identical elements.Reference numerals that are introduced in the specification inassociation with a figure may be repeated in one or more subsequentfigures without additional description in the specification in order toprovide context for other features, and not every element may be labeledin every figure. The drawings are not necessarily to scale, emphasisinstead being placed upon illustrating embodiments, principles andconcepts. The drawings are not intended to limit the scope of the claimsincluded herewith.

FIG. 1 shows an exploded view of internal components of an example axialflux machine with a planar stator;

FIG. 2 shows a sectioned view of an axial flux machine including thecomponents shown in FIG. 1 ;

FIG. 3 shows an example planar stator that may be employed in an axialflux machine, such as the axial flux machine shown in FIGS. 1 and 2 ;

FIG. 4 shows a schematic view of the disposition of materials in acomposite structure for a conventional printed circuit board;

FIG. 5 shows a schematic view of how several of copies of the compositestructure shown in FIG. 4 may be repeated in the stack-up of aconventional composite printed circuit board;

FIG. 6 shows a composite structure (e.g., for use in a planar stator) inwhich a magnetic composite material is disposed in the intersticesbetween copper features;

FIG. 7 illustrates how the composite structure of FIG. 6 may beimplemented as a repeat unit to construct a practical composite printedcircuit board in accordance with some embodiments of the presentdisclosure; and

FIG. 8 is a cross section view of a sample from a planar stator, withsix conductive layers, showing the deposition of a magnetic compositematerial in the interstices between radial traces.

DETAILED DESCRIPTION

Unlike machines of conventional construction, in which the armature isoften wound using wire on a soft magnetic material core, the windings ina printed circuit board stator (e.g., as described in the '625 patentand the '953 patent incorporated by reference above) are supported by anon-magnetic composite material. This composite typically consists of afiberglass cloth, epoxy, and copper for the winding and thermalstructure. Accordingly, machines of this type are often described as“air core” machines.

The inventors have recognized and appreciated that such planar printedcircuit board stators can be improved significantly by introducing oneor more soft magnetic materials into the stator substrate. Severalexamples of planar circuit board stators enhanced with such softmagnetic material(s), as well as several example techniques forproducing such stators, are described herein.

FIGS. 1 and 2 show exploded and sectioned views, respectively, of aplanar stator axial flux machine 100 of the type disclosed in the '625patent and the '953 patent. As shown in these figures, a planar stator102 may be placed in the gap of a magnetic circuit established bycomponents of a rotor. FIG. 3 shows a top view of an example planarstator 102 that may be employed in the machine 100. As shown best inFIG. 1 , the rotor may include magnets 104 a, 104 b and supportstructures 106 a, 106 b that together form a pair of rotor assemblies108 a, 108 b that may be attached to a shaft 110 of the rotor. As shownin FIG. 2 , an outer edge 112 of the planar stator 102 may be fixedlysecured to a housing 114 (e.g., by being held between respectivesections 114 a, 114 b of the housing 114), whereas the rotor shaft 110(to which the rotor assemblies 108 a, 108 b are attached) may berotatable relative to the housing 114 (e.g., via bearings 116).

As shown in FIG. 3 , the planar stator 102 may include radial traces302. The portion of the planar stator 102 with such radial features,i.e., the annular region extending between a radial distance r1(measured from a center point 304 of the planar stator 102, whichcoincides with the axis of rotation of the rotor of the machine 100) anda radial distance r2 (also measured from the center point 304), islocated within the “active” area of the machine 100, in the sense thatit is primarily responsible for the production of torque in the machine100. The inner and outer radii of the magnets 104 attached to the rotorof the machine 100 are typically positioned at or near the radialdistance r1 (measured from stator's axis of rotation) and the radialdistance r2 (also measured from the stator's axis of rotation),respectively, thus creating axially directed magnetic flux within theannular active area. The remaining features, e.g., inner end turns 306and outer end turns (which may be on a different layer of the planarstator 102) radially adjacent to the annular active area of the planarstator 102, may exist only to connect the radial traces 302 in seriesand parallel combinations and convey the associated currents andvoltages to terminals 308 of the planar stator 102.

In motor mode, a current density that rotates synchronously about therotor's axis of rotation may be imposed on the planar stator 102 by acontroller 118 (shown in FIG. 1 ). The interaction of this currentdensity with the magnetic flux in the gap from the rotor assemblies 108a, 108 b leads to a torque of electromagnetic origin. The controller 118may be operated such that the energy conversion effected by thisstructure is bidirectional, in the sense that the electric machine mayabsorb power from the mechanical terminals and deliver it to theelectrical terminals, or it may deliver power to the mechanicalterminals. Under appropriate control, a machine of this kind maysimulate a variety of mechanical loads including components of friction,moment of inertia, and similar.

FIG. 4 shows a schematic view of the disposition of materials in acomposite structure 400 for a conventional printed circuit board withrelatively high-profile traces. Such a structure may be used, forexample, to form a conventional planar stator for an axial flux machine,such as the planar stator 102 of the axial flux machine 100 shown inFIGS. 1-3 . The stack-up indicated in FIG. 4 focusses on the interfacebetween two layers 402 a, 402 b of copper-clad material (e.g., apre-fabricated glass-epoxy, copper sheet) and the opposing copperfeatures 404 etched on the two copper-clad layers. In someimplementations, for example, each of the layers 402 may be formed byetching a respective copper clad laminate (CCL) sheet, such as FR-4 CCL,to form the copper features 404. As illustrated, each layer 402 mayinclude a dielectric core layer 406 (e.g., a fiberglass cloth) to whichan etched copper sheet (including the copper features 404) is adhered(e.g., via an epoxy resin). Although not shown in FIG. 4 , it should beappreciated that the opposite sides of the illustrated dielectric corelayers 406 may likewise have copper sheets (possibly etched to formadditional copper features 404) adhered to them. Etched CCL sheets ofthis type may be used, for example, to form the composite printedcircuit board structures 500, 700 described below in connection withFIGS. 5 and 7 . The copper features 404 may, for example, correspond toradial traces 302 within an “active area” of the planar stator 102 thatextends between a first radius r1 and a second radius r2, as illustratedin FIG. 3 .

As shown in FIG. 4 , to bond the respective layers 402 a, 402 btogether, achieve a flat composite structure 400, and provide dielectricbetween the opposing copper features 404, several layers of “prepreg”408 may be inserted between the etched copper surfaces. “Prepreg” is anepoxy impregnated glass fiber cloth. As illustrated, epoxy 410 from theprepreg 408 may flow out of the high-profile contact areas into theinterstitial space between the active-area traces. Sufficient prepregmay be employed so that the interstitial space can be filled when thecomposite structure 400 is compressed and bonded together.

FIG. 5 shows a schematic view of how several of copies of the compositestructure 400 shown in FIG. 4 may be included in the stack-up of atypical composite printed board structure 500 with, in this example,twelve layers of conductive materials including, e.g., copper features404.

In simplest terms, in a machine of the type shown in FIGS. 1 and 2 , therotor supports a magnetic circuit in a rotating frame with a gap. Theplanar stator 102 is positioned within the gap, and windings on theplanar stator 102 link flux from the rotor. Under quiescent conditions,the solution for the flux in the gap is essentially independent of thepresence of the planar stator 102 because the materials used in thestator construction (e.g., the dielectric core layer 406, the prepreg408, and the epoxy 410 shown in FIGS. 4 and 5 ) have a magneticpermeability that is essentially the same as free space, or “air.”Machines of more conventional construction integrate the windings withsoft magnetic material, often made from laminations of special steels.This material participates in the magnetic circuit. However, when softmagnetic structures are integrated with the stator in a permanent magnetbrushless machine, for example, the steel is subjected to significanttime-varying magnetic flux that tends to drive a variety of lossmechanisms in the soft magnetic material. This is one of the reasonsthat the materials used in such machines are typically made of laminatedstampings that reduce the losses associated with eddy currents in themagnetic material. There are a number of disadvantages that come withthe incorporation of soft magnetic materials in a typical steellamination construction, including tooling costs, winding limitations(fill factor), electrical and acoustic noise, electrical insulationrequirements, quality of motion, and thermal concerns.

An advantage is that the utilization of a core can reduce, or in somecases eliminate, the need for economically sensitive rare earth hardmagnetic materials. Additionally, and independent of the hard magneticmaterials, incorporating a core may improve some aspects of performancein a tradeoff with others. Consider, for purposes of illustration, alossless machine with a transformation of electrical variables to therotating frame—an ideally commutated machine. In this situation, themachine is characterized by a single constant that relates torque tocurrent (K_(t)) and voltage, or back EMF, to speed (K_(v)). Inappropriate units and quantities, these constants are equal. If theconstant is made larger, a smaller current will provide a given torque,and a lower speed will result in a given terminal voltage.

The back EMF of the machine, and the constant which relates the machinecurrent to torque, can be deduced by the flux linked by the turns. Inparticular, as a consequence of Maxwell's equations in themagnetoquasistatic case, turns linking a flux λ contribute a voltage

$v_{t} = {\frac{d}{dt}\lambda}$

Further, if the flux linked by the static geometry of the turns (in thestator) is changed by virtue of the orientation of the rotor at angle θwith respect to the stator, then the equation above becomes

${v_{t}(\theta)} = {\frac{d\lambda}{d\theta}{\frac{d\theta}{dt}.}}$

The term

$\frac{d\lambda}{d\theta}$has two components to consider in a permanent magnet machine. One sourceof flux λ₁ contributing to

$\frac{d\lambda}{d\theta}$originates with the magnets fixed in the rotor (θ being the angle of therotor) and the solution of the associated magnetic circuit. This is theterm most important in the air-core machine. Another component λ₂contributing to

$\frac{d\lambda}{d\theta}$involves the change of flux linked from the turns themselves. For thiscomponent, λ₂=L(θ), which may be thought of as angle-dependentinductance.

At a fixed speed,

${\frac{d\theta}{dt} = \omega},$and steady-state conditions, the significance of

$\frac{d\lambda}{d\theta}$is that it provides a relationship between speed and voltage thatdetermines the performance characteristics of the electric machine. Thiscan be analyzed piece-by-piece, e.g., the voltage of the winding is thesuperposition of the

$\frac{d\lambda}{d\theta}$ω contributions of the components of the winding.

As

$\frac{d\lambda}{d\theta}$is a function of θ, and is thus periodic, it has a Fourier series. Insome cases,

$\frac{d\lambda}{d\theta}$terms may be well approximated by the first term of the series. In thiscase, the terminal voltage for a machine that has n poles andmechanically rotates at a frequency ω can be written,v(t)≈K sin(nωt+θ ₀)ω.

In this equation, ω is the mechanical frequency of rotation, n is thepole count of the machine, nω is the electrical frequency, t is time, θ₀is an angular offset, and K sin(nωt+θ₀) is the first term of the Fourierseries approximating

$\frac{d\lambda}{d\theta}$over the winding. Commutation of the machine effectively removes thesinusoidal dependency, and exposes K—with contributions from hardmagnetic materials, the solution for the linked flux, and the θdependent inductance terms—as the factor that can cause the machine toproduce more voltage per unit speed, and more torque per amp. Additionof a soft magnetic core material to an air-core machine can increase thecomponents contributing to

$\frac{d\lambda}{d\theta},$and thus generally increase K for the machine.

One possible way to introduce a soft magnetic core material to anair-core machine is to replace the fiberglass substrate supporting theelectrically conductive traces (e.g., the dielectric core layer of aconventional a CCL sheet) with a soft magnetic material. This materialmay be non-conductive and relatively stiff, e.g., a ceramic insulator,such as a soft ferrite. Since the material would be exposed totime-varying magnetic fields in the course of operation of the machine,low-loss magnetic characteristics would be desirable. To produce acircuit board structure with a ceramic insulator or the like as thesupporting substrate, a planar conductive layer (e.g., a copper layer)may be disposed on either or both surfaces of a planar sheet of theceramic insulator material to generate a structure similar to a CCLsheet, and such conductive sheet(s) may then be etched, e.g., usingstandard printed circuit board (PCB) processes, to form patterns for thewindings of the poles of an armature and/or other conductive traces.

The properties of the families of materials that meet these criteria,such as difficulty in machining, may mitigate towards implementationsthat reduce the number of layers needed to form a planar windingstructure. The winding structures disclosed in the '953 patent,incorporated by reference above, can be achieved in as few as twoconductive layers. There may also be advantages to using a soft magneticmaterial as a substrate to support the windings of a planar stator interms of the allowable thermal conditions.

Another possible way to introduce a soft magnetic core material to anair-core machine is to integrate magnetic core material with a printedcircuit board as part of the manufacturing process. Such animplementation has the advantage of retaining the techniques and windingprocedures of planar stators designed for the printed circuit boardprocesses, as well the inherent precision and scalability associatedwith such processes. In some such implementations, one or more powderedsoft magnetic materials may be combined with one or more carriermaterials that are otherwise used as “fill” in the printed circuit board(e.g., a low-viscosity epoxy product) to form a magnetic compositematerial. Such a magnetic composite material may thus form a softmagnetic core, resulting in a planar armature with a dielectricsubstrate that supports conductive traces and also has integral softmagnetic material in (at least) the locations where it is needed.

FIG. 6 shows an example composite structure 600 (e.g., for use in aplanar stator 102) in which a dielectric substrate (including thedielectric core layers 406, the magnetic composite material 602, and theprepreg 408) supports conductive traces (i.e., the copper features 404),and in which the magnetic composite material 602 is disposed in theinterstices between the copper features 404 (e.g., corresponding to theradial traces 302 shown in FIG. 3 ). The composite structure 600 can becompared to the composite structure 400 shown in FIG. 4 in which theprepreg 408 and associated epoxy 410 is instead disposed in theinterstices between the copper features 404. Since, in the compositestructure 600, these interstices are filled with the magnetic compositematerial 602, the need for prepreg 408 to fill those spaces may bereduced. As such, in some implementations, prepreg 408 may be used onlyto meet the dielectric requirement of the planar stator 102, i.e.,electrical insulation between axially close copper features 404. In someimplementations, for instance, only a single layer of prepreg 408 may bedisposed between the two layers 402 a, 402 b of etched copper-cladmaterial. FIG. 7 shows a schematic view of how several of copies of thecomposite structure 600 shown in FIG. 6 may be included in the stack-upof a novel composite printed board structure 700 with, in this example,twelve layers of conductive materials, e.g., including copper features404, and integral soft magnetic material, e.g., the magnetic compositematerial 602 that is positioned in the interstices between the copperfeatures 404.

As noted above, FIG. 3 shows a top view of a typical a planar stator 102including traces forming stator windings. The active area of the planarstator 102, which is where the rotor axial flux is imposed, is describedby an annulus between radii r₁ and r₂. As shown, the active area of theplanar stator 102 may include the radial traces 302. In someimplementations, the magnetic composite material 602 described hereinmay be placed only within this active area, e.g., in the intersticesbetween the radial traces 302. In other implementations, the magneticcomposite material 602 may additionally or alternatively be placed inother regions of the planar stator 102.

Powdered soft magnetic materials are widely available for themanufacture of components, such as chokes, inductors, and transformers.Examples of products formed using such powdered soft magnetic materialsinclude Kool Mu (sendust), MPP (molypermalloy), Kool Mμ MAX, Kool Mu_Hf,Edge, High Flux, XFlux, and 75-Series, all available from Magnetics,which has headquarters in Pittsburgh, Pa. In these conventionalapplications, the powders are often sintered or bonded to form cores,either with embedded wires or as forms around which wires can be wound.Powdered soft magnetic materials of this type are available from anumber of sources. Examples include 40337 Iron powder, 00170 Ironpowder, and 10214 Iron powder, available from Alfa Aesar (part of ThermoFisher Scientific) of Tewksbury, Mass.

Eddy current losses in components that include such powdered softmagnetic materials can be controlled via particle size because theinterfaces between conductive grains can be made sparse, i.e., so thatthe particles tend not to form larger conductive networks. Magneticlosses decrease with particle size as well, relative to a bulk sample ofthe same material, as the collection of grains approximates individualdomains with fewer domain-to-domain interactions. As the materialparticle size becomes extraordinarily small (nano-scale, e.g., between 1and 100 nanometers), new effects may be apparent. These effects aregenerally beneficial from the magnetic point of view, but may presentchallenges from the point of view of handling, mixing, and reactivitywith materials for integration in the printed circuit board environment.

In some implementations, to introduce powdered soft magnetic materials,such as those identified above, into printed circuit board stators, aprocedure may be used in which one or more such soft magnetic powdersare mixed with one or more low-viscosity epoxy products compatible withprinted circuit board materials and processes to form a magneticcomposite material 602, as described above. In some implementations,soft magnet powder(s) having an optimal magnetic particle size for agiven application may be selected and/or such soft magnetic powder(s)may be screened to control the size of the magnetic particles that areused. In some implementations, for example, magnetic powder(s) having anaverage magnetic particle size (e.g., diameter) of 1 micrometer (μm), or2 μm, or 5 μm, or 10 μm, or 20 μm, or 50 μm, or 100 μm may be employed.Further in some implementations, such magnetic powder(s) mayadditionally or alternatively be screened such that the maximum size(e.g., diameter) of the magnetic particles they contain is less than 100μm, or less than 50 μm, or less than 20 μm, or less than 10 μm, or lessthan 5 μm, or less than 2 μm, or less than 1 μm. As noted above, eddycurrent losses in these materials can be managed by controlling the sizeof the soft magnetic particles so as to cause the interfaces betweenindividual particles to become sufficiently sparse. Further, by keepingthe magnetic particles sufficiently small and/or sparse, the magneticcomposite material 602 can be made non-conductive in the bulk, eventhough individual magnetic particles might themselves be conductive insome implementations. The magnetic composite material 602 may thus serveas an insulator between individual conductive traces 302, 404 of aplanar stator 102.

An example of a low-viscosity epoxy product that may be mixed with suchmagnetic powder(s) to form a magnetic composite material 602 is theEMP110 Photoimageable Soldermask available from Electa Polymers Ltd. ofKent, England. Such a magnetic composite material 602 may then bedispensed with standard processes into volumes in the printed circuitboard (e.g., in in the interstices between copper features 404) thatwould otherwise be filled with other materials (e.g., layers of prepreg408 and/or epoxy 410) in the process of manufacture. The result of thisapproach is a composite printed circuit board structure, e.g., thecomposite printed board structure 700 shown in FIG. 7 , thatincorporates low-loss magnetic material, e.g., the magnetic compositematerial 602.

In some implementations, to make a planar composite stator integratingone or more powdered soft magnetic materials in the interstices betweentraces, e.g., the radial traces 302 shown in FIG. 3 , there are twoprinciple steps that may be employed in the processing of one of thecopper clad repeat units, e.g., one of the layers 402 shown in FIG. 6 ,of the assembly. A first such step may be to place the soft magneticmaterial, e.g., the magnetic composite material 602, in the desiredlocations, and to place a non-magnetic filler material in the locationswhere magnetic material is not wanted. An example of non-magnetic fillermaterials suitable for this purpose is the EMP110 PhotoimageableSoldermask noted above. In the construction of a planar armature, it maybe desirable to confine the soft magnetic material, e.g., the magneticcomposite material 602, to the active area of the stator (between r1 andr2 in FIG. 3 ) in which the interaction with the rotor is significant. Asecond such step may be to planarize the layers 402 so they may be“stacked” with uniform results. Permutations of the techniques describedfor these steps may have similar results.

In some embodiments, individual CCL sheets, e.g., FR-4 CCL panels, maybe etched with the desired winding pattern, as would be done for aconventional planar stator, e.g., a planar stator of the type describedin the '625 and '953 patents incorporated by reference above. A mixtureof one or more epoxies and one or more powdered soft magnetic materials,e.g., the magnetic composite material 602 described above, may then bescreened or placed via a computer controlled dispenser onto the activeareas of the etched CCL sheets, e.g., between the copper features 404forming the radial traces 302 of the planar stator 102 shown in FIG. 3 .In some implementations, the magnetic composite material 602 may beexcluded from the areas in which it is not desired, e.g., outside theactive area of the planar stator 102, by depositing and partially curinga non-magnetic filler material in these areas prior to depositing themagnetic composite material 602 on the etched CCL sheets. The uncuredmaterial may then be mechanically leveled, for example, with a doctorblade. As a result of these processes, some material may lie on thecopper traces and may extend beyond the level of the trace tops.

In other embodiments, individual CCL sheets, e.g., FR-4 CCL panels, mayfirst be etched with an initial pattern so as to leave voids at desiredlocations for subsequently introduced magnetic material. A mixture ofone or more epoxies and one or more powdered soft magnetic materials,e.g., the magnetic composite material 602 described above, may then bescreened, computer dispensed, or dispensed in bulk onto the initiallyetched CCL sheets and leveled, for example, with a doctor blade. As aresult of these processes, some material may lie on the portions of thecopper of the CCL sheets that will form the traces for the planar stator102. A subsequent etch of the remaining pattern may produce theinterstices and voids required for the stator circuit traces that arenot desired to be filled with magnetic material. Such voids may then befilled with a non-magnetic filler material, e.g., of the type describedabove. The sequence of these etch and fill steps may be interchanged insome implementations.

Following the steps above, excess non-magnetic fill material may need tobe removed to allow the assembly of a uniform sequence of layers 402.Since the copper traces for the planar stator 102 may be describedaccurately by the Gerber code used to prepare CCL sheets with a patternof traces, in some implementations, the same code may be translated to acontrol sequence for a laser that can oblate the magnetic compositematerial 602 and level the surface. An appropriate laser for thisprocess may be effective at removing epoxy materials, e.g., the magneticcomposite material 602 or the non-magnetic fill material describedabove, but may be stopped by the underlying copper trace. Such lasersare employed in standard PCB manufacturing to make connections to innerlayers in printed circuit boards. In other implementations, the magneticcomposite material 602 and/or the non-magnetic fill material may insteadbe brought to a state of cure where it is possible to economically andeffectively planarize the layer mechanically to remove excess material.

The techniques disclosed herein can also be applied to make planarprinted circuit board armatures that are thinner as compared toequivalent stators made using conventional techniques. This result maybe achieved, for example, by filling the interstitial gaps with epoxy,rather than epoxy loaded with magnetic material. Similar steps to levelthe surface and remove excess material may be used in suchimplementations. A reduced number of layers of pre-impregnated cloth,e.g., the prepreg 408 described above, can then be used in the stack up.

Features and Benefits of Integrating Soft Magnetic Core Materials

The integration of core material in an electric machine has a number ofbenefits, some of which have been previous noted. In particular, theconstruction here can be automated in construction of the PCB, incontrast to methods that require placing discrete magnetic cores inslots and/or holes in the PCB. The magnetic material may be effectivelysecured in the PCB matrix.

In a motor application, the presence of core material may allowsubstitution of lesser grade magnets and/or the use of less magneticmaterial relative to a similar air-core design. Tradeoffs in quality ofmotion, harmonics and other motor parameters may also be involved. Thepresence of core material may allow more effective use of armaturereaction, for example, in field weakening applications.

A down side of the technique is that, unlike an air core machine, thereis a magnetic force of attraction between the stator and rotor underquiescent conditions. In the center of the gap, the magnetic materialfilled stator may be at an unstable equilibrium point. This may require,for example, stator geometries that are inherently stiffer relative toair-core designs.

There are numerous market opportunities for motors and generators thatwork well with inexpensive magnets or where very high torque density isneeded.

The benefits of the incorporation of magnetic material described heremay apply to other kinds of electromagnetic devices and circuitelements. For example, inductors, transformers, inductive sensors, andenergy harvesting devices with PCB traces windings may benefit fromembedded core materials.

The technique of filling the interstitial gaps with soft magneticmaterial may also be employed to make a printed circuit boards(including planar armatures) with high-profile copper features withreduced over-all thickness. This has been reduced to practice. In atypical sample, a stator with conventional stack-up and constructionwith a thickness of 0.0920 inches was remade using this process,resulting in a thickness of 0.0695 inches. Reduced stator thickness mayconvey a variety of closely linked machine performance tradeoffs andbenefits, including reduced magnet usage, higher efficiency, increasedperformance, reduction in losses, and/or enhanced thermal performance.

FIG. 8 is a cross section view of a sample from a planar stator, withsix conductive layers, showing the deposition of a magnetic compositematerial 602. The magnetic composite material 602 used to fill theinterstices between radial traces 302 was formed using a powdered softmagnetic material that was screened to a maximum size of 25 μm and thenmixed with a low-viscosity epoxy product, as described above. The areasincluding magnetic particles and the epoxy matrix in which suchparticles are secured are evident. In this prototype, the thickness ofthe prepreg 408 was not reduced to the extent possible. If this had beendone, it would have substantially increased the relative content ofmagnetic composite material 602 between the radial traces 302.

Having thus described several aspects of at least one embodiment, it isto be appreciated that various alterations, modifications, andimprovements will readily occur to those skilled in the art. Suchalterations, modifications, and improvements are intended to be part ofthis disclosure, and are intended to be within the spirit and scope ofthe disclosure. Accordingly, the foregoing description and drawings areby way of example only.

Various aspects of the present disclosure may be used alone, incombination, or in a variety of arrangements not specifically discussedin the embodiments described in the foregoing and is therefore notlimited in this application to the details and arrangement of componentsset forth in the foregoing description or illustrated in the drawings.For example, aspects described in one embodiment may be combined in anymanner with aspects described in other embodiments.

Also, the disclosed aspects may be embodied as a method, of which anexample has been provided. The acts performed as part of the method maybe ordered in any suitable way. Accordingly, embodiments may beconstructed in which acts are performed in an order different thanillustrated, which may include performing some acts simultaneously, eventhough shown as sequential acts in illustrative embodiments.

Use of ordinal terms such as “first,” “second,” “third,” etc. in theclaims to modify a claim element does not by itself connote anypriority, precedence or order of one claim element over another or thetemporal order in which acts of a method are performed, but are usedmerely as labels to distinguish one claimed element having a certainname from another element having a same name (but for use of the ordinalterm) to distinguish the claim elements.

Also, the phraseology and terminology used herein is used for thepurpose of description and should not be regarded as limiting. The useof “including,” “comprising,” or “having,” “containing,” “involving,”and variations thereof herein, is meant to encompass the items listedthereafter and equivalents thereof as well as additional items.

What is claimed is:
 1. A planar armature for an axial flux machine, theplanar armature comprising: a first layer comprising a first dielectricsubstrate; a second layer comprising a second dielectric substrate; anda third layer disposed between the first layer and the second layer,wherein the third layer comprises: first conductive traces that form atleast first portions of windings for at least a first pole of the planararmature, a first quantity of a magnetic composite material disposed ininterstices between the first conductive traces within at least a firstregion of the third layer, wherein the magnetic composite materialcomprises particles of a soft magnetic material embedded within a firstdielectric material and the first region is located within an activearea of the axial flux machine, and a second quantity of a seconddielectric material disposed within at least a second region of thethird layer, wherein the second dielectric material is free of the softmagnetic material and the second region is located outside of the activearea.
 2. The planar armature of claim 1, wherein the soft magneticmaterial comprises a powdered soft magnetic material.
 3. The planararmature of claim 2, wherein the first dielectric material comprises anepoxy.
 4. The planar armature of claim 1, wherein a maximum diameter ofthe particles is 50 micrometers or less.
 5. The planar armature of claim1, wherein at least a portion of the magnetic composite material isdisposed within etched regions of a copper clad laminate sheet.
 6. Theplanar armature of claim 1, wherein: the first conductive tracescomprise radial conductive traces within the active area, and themagnetic composite material is disposed in interstices between theradial conductive traces.
 7. The planar armature of claim 3, wherein thesecond dielectric material comprises an epoxy.
 8. The planar armature ofclaim 1, wherein the second dielectric material comprises an epoxy. 9.The planar armature of claim 1, wherein: the first dielectric substrateand the first conductive traces are components of a first etched copperclad laminate sheet; the second dielectric substrate is a component of asecond etched copper clad laminate sheet, wherein the second etchedcopper clad laminate sheet includes second conductive traces that format least second portions of the windings for the first pole of theplanar armature; and the second conductive traces are disposed on afourth layer of the planar armature, the fourth layer being disposedbetween the second layer and the third layer.
 10. The planar armature ofclaim 9, further comprising: a fifth layer comprising prepreg, the fifthlayer being disposed between the third layer and the fourth layer. 11.The planar armature of claim 10, further comprising: a third quantity ofthe magnetic composite material disposed in interstices between thesecond conductive traces within at least a third region of the fourthlayer, wherein the third region is located within the active area of theaxial flux machine, and a fourth quantity of the second dielectricmaterial disposed within at least a fourth region of the fourth layer,wherein the fourth region is located outside of the active area.
 12. Theplanar armature of claim 11, wherein: the first conductive traces aredisposed on a first side of the first etched copper clad laminate sheet;and third conductive traces are disposed on a second side of the firstetched copper clad laminate sheet opposite the first side, wherein thethird conductive traces are disposed in a sixth layer of the planararmature and form at least third portions of the windings for the firstpole of the planar armature.
 13. The planar armature of claim 12,further comprising: a fifth quantity of the magnetic composite materialdisposed in interstices between the third conductive traces within atleast a fifth region of the sixth layer, wherein the fifth region islocated within the active area of the axial flux machine, and a sixthquantity of the second dielectric material disposed within at least asixth region of the sixth layer, wherein the sixth region is locatedoutside of the active area.
 14. The planar armature of claim 9, furthercomprising: a third quantity of the magnetic composite material disposedin interstices between the second conductive traces within at least athird region of the fourth layer, wherein the third region is locatedwithin the active area of the axial flux machine, and a fourth quantityof the second dielectric material disposed within at least a fourthregion of the fourth layer, wherein the fourth region is located outsideof the active area.
 15. The planar armature of claim 1, wherein: thefirst dielectric substrate and the first conductive traces arecomponents of a first etched copper clad laminate sheet; and the seconddielectric substrate comprises prepreg.